Potential Use of Proteinase Inhibitors, Avidin, and other Bio-reagents for Synergizing Bt Performance and Delaying Resistance Development to Bt

Abstract

After being ingested by target insects, the insecticidal proteins from Bacillus thuringiensis (Bt) need to go through a proteolytic process by insect midgut proteinases to become activated. At the same time, Bt can be hydrolyzed and degraded by midgut proteinases to become non-toxic to target insects. Once activated, the Bt proteins need to bind to midgut brush border membrane vesicle (BBMV) to cause gut lining lesions and eventually death in the target insect. A few bio-reagents may interact with the Bt binding to the receptors. By applying proteinase inhibitors to Bt-containing (sublethal dose) diet, the growth and development of Helicoverpa zea were significantly decreased when compared with the Bt only control. Midgut samples tested against the substrates for major midgut enzymes showed significant decreases in the protease activity of larvae fed Bt plus inhibitor versus control. Avidin, causing sequestration of biotin and vitamin deficiency, potentially interacts with Bt by binding to biotin-containing proteins. Besides possessing insecticidal toxicity itself, avidin at a sublethal dose could significantly synergize Bt toxicity against H. zea larvae. Because of different modes of action from that of Bt, proteinase inhibitors, avidin, and other bio-reagents could be used to enhance Bt performance, delay resistance development to Bt, and expand control range beyond lepidopterans.